An electrically writable/rewritable EEPROM can find extensive applications because it allows on-board rewrite and rewrite in units of pages or bytes. To be adapted for such extensive applications, the EEPROM is required of high reliability design and further miniaturization.
As a known miniaturizing technique for EEPROM, Patent Document 1, for example, proposes a technique of achieving miniaturization by preventing the degradation of tunnel oxide.
Patent Document 2 proposes a technique of miniaturizing memory cell by forming a microscopic tunnel window.
Further, Patent Document 3 proposes a technique of miniaturizing a floating gate.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2007-013197    Patent Document 2: Japanese Unexamined Patent Application Publication No. 2005-183763    Patent Document 3: Japanese Unexamined Patent Application Publication No. 2005-005731